Queen Elizabeth II's second son Prince Andrew received substantial sums of money from a Turkish businessman who is accused of fraud by a millionaire compatriot, court documents show.

Andrew is not himself accused of wrongdoing, but the allegations bring unwelcome new publicity after he settled a US civil claim for sexual assault.

Turkish woman Nebahat Isbilen alleges that businessman Selman Turk told her in November 2019 that she had to make a "gift" of £750,000 for Andrew's help to obtain a UK passport.

The documents from a High Court civil claim brought by Isbilen in London conclude that the purported passport offer was a ruse by Turk, newspaper reports said Friday.

Andrew has repaid the £750,000, the Daily Telegraph and Daily Mail said. He declined to comment on the case, or to explain to Isbilen's lawyers the nature of his relationship with Turk. 

The Duke of York's ex-wife Sarah received at least £225,000 in return for acting as a "brand ambassador" for one of Turk's companies, the Telegraph said. 

A spokesman for Sarah said she was "completely unaware of the allegations that have since emerged against Mr Turk".

Andrew and Sarah have long been dogged by accusations of poor judgment in their financial dealings and relationships with wealthy acquaintances.

Isbilen, who is in her 70s, says she turned to Turk for help to get her fortune out of Turkey after her husband was jailed in 2015 on what he says were politically motivated charges.

She claims that Turk misappropriated around $50 million. He denies it.

The case has yet to come to trial but preliminary rulings have been published by the judge, which revealed the involvement of Andrew and Sarah.

Andrew, 62, has rarely been seen since a disastrous 2019 interview in which he defended his friendship with Jeffrey Epstein, a US financier and convicted sex offender who killed himself in prison.

But he appeared in public on Tuesday accompanying his mother at a televised memorial service for his late father, Prince Philip.

It was his first public appearance since settling the assault brought in New York by Virginia Giuffre in February. 

In January, the queen stripped him of his honorary military titles, effectively removing him from any official role.